Geology is a science that consists of studying the parts of the Earth accessible to observation and developing hypotheses that make it possible to reconstruct their history and explain their layout.
It is above all a field science, as evidenced by the classic image of the geologist armed with a hammer to take samples, a magnifying glass to make a first examination, pencils, a notebook and a card, to write down what he sees.
Geology, earth science
Geology is a scientific discipline focusing on the outer layers of the Earth, including their structure, composition and evolution over time past and future.
Therefore, geology is made up of many specialized disciplines, such as mineralogy, paleontology, petrology, geodynamics, geomorphology, etc.
It is practiced by geologists, who must daily exploit other sciences to achieve their goal, mainly chemistry and physics. This science of the Earth would have seen its foundations born around 1660.
Geology of a region
The term geology is also used generically to refer to the characteristics of the subsoil of a given region, which can also be observed on geological maps.
To take advantage of their samples and his observations, the geologist must rely on several complementary disciplines
Here are the most common examples:
- petrography (study of rocks, based on mineralogy and crystallography)
- volcanology (study of volcanoes)
- sedimentology (study of how sediments are deposited)
- geochemistry (study of the chemical behavior of elements)
- stratigraphy (study of the succession of sediments)
- tectonics (study of the deformations of the surface part of the Earth)
- paleontology (study of fossils)
- geomorphology (study of reliefs)
- applied geology, which uses these different disciplines in areas of interest such as mining, oil, public works, water, etc.
Different related disciplines
Geology has many ties with other sciences, among which it is worth mentioning:
- crustal geochemistry, which studies the chemistry of the Earth’s surface layers; deeper layer geochemistry is more about internal geophysics, or earth physics, than about geology;
- geophysics, organized internationally in the International Union of Geodesy and Geophysics (IUGG), which studies the structure and internal composition of the Earth with tools borrowed from physics and mathematics; unlike the geological and mineral sciences, which are essentially descriptive and qualitative sciences, the geophysical sciences are ranked among the exact and quantitative sciences; geologists often understand under the term “geophysics” only applied geophysics (including seismic, gravimetric, magnetic, electrical, electromagnetic methods, … applied to oil and mining prospecting, archeology, environmental studies, etc. ); hydrogeophysics is part of the latter;
the seismic engineer who deals with macroseismic studies in the field following an earthquake of some importance; it is also responsible for assessing seismic risk and setting paraseismic standards for a given country or region; it also participates in the surveillance of regions at risk and, if possible, tries to predict future earthquakes, either by statistical methods, or by deterministic methods when possible;
- paleoseismology is a branch of seismology directly dependent on geology; its purpose is to find in trenches or geological sections indications of ancient earthquakes, to date them so that they can be used in the statistical forecasting of earthquakes, and to provide geophysicists with information allowing them to be quantified (focus mechanism, magnitude , seismic moment, …) these ancient earthquakes;
- hydrogeology, which studies the flow of groundwater, knowing that the nature of the subsoil through which the water flows directly influences the quantity and quality of the water emerging at the source or extracted from the borehole;
- geomorphology, which studies the forms of the earth’s relief; it is considered to concern the geographer more than the geologist, and is most often ranked among the branches of physical geography;
- mineralogy, which studies the nature, composition and physical properties of the minerals that make up rocks;
- paleontology, which studies past organisms through the description and analysis of fossilized remains;
- morphotectonics, which studies the morphological consequences of tectonic and erosion processes;
micropaleontology, which studies microscopic fossils contained in sediments;
petrology, which studies the mechanisms that preside over the genesis and transformation of rocks;
petrography, which describes the nature of rocks and analyzes their structural, mineralogical and chemical characteristics;
- sedimentology, which studies rocks and sedimentary formations; in this case we also speak of stratigraphy which studies the succession of the different geological layers or strata;
- seismology, which studies earthquakes and the propagation of natural or induced seismic waves (we then speak of seismic); this discipline is an important branch of geophysics, and only some of its results interest the geologist;
- volcanology, which analyzes and attempts to predict volcanic phenomena, which studies the chemical and mineralogical composition and the processes of setting up volcanic products;
structural geology, which is the study of the deformations of rocks and the mechanisms governing the deformation of these rocks at all scales; on a large scale, we speak of tectonics;
- metallogeny, which studies the mechanisms of formation of metalliferous deposits and sets out to define methodological tools and prospecting guides that can be used by explorers and mining prospectors;
- geoarchaeology, which studies archaeological sediments and deposits from the Quaternary age;
- exogeology or astrogeology which, through remote sensing methods, in situ or laboratory experimentation and the collection of samples, studies the composition, structure and history of the surface of the planets of the solar system and their natural satellites, aeology deals more particularly with the planet Mars. However, planetary geology is the most used term;
- geotechnics, which works on the mechanics of rocks and soils upstream of civil engineering;
- geodesy, which studies the shape and dimensions of the Earth; this one is an exact science, twin sister of astronomy, which by its gravimetry part is among the disciplines of geophysics;
- speleology, concerns the study of natural cavities, most often in karstic zones; this study encompasses the geological knowledge of the surrounding terrain.